Over the past ten or so years, there has been considerable research focused on developing lightweight concrete for structural purposes due to its obvious benefits including lightweight, exceptional heat and sound insulation. It has been recognized that the quality of concrete structures and enhancing the service life of structural products that the structures are therefore improved especially in areas of hazardous environmental conditions.
In considering harsh chemical conditions, the resistance of concrete to chloride penetration and the erosion rate of steel reinforcements during the lifespan of the structure are initial concerns. In the present case, Applicants' initial focus was on the durability of concrete structures and an ability to function within harsh environmental conditions and utilizing perlite aggregates together with silica fume to produce a lighter weight product.
An initial patentability search disclosed several approaches. For example, a publication from 1977, CH 585680 discloses a light concrete mortar preparation by adding expanded perlite and/or expanded clay or slate aggregates to cement binders having a dense structure and a bulk weight of 950-1200 kg/m3 and compressive strength of about 140-180 kp/cm2 was prepared by mixing cement and binders with ≥aggregates from expanded perlite and expanded clay, slate and/or etc. and water.
The mortar can be cast or molded to boards or other constructional materials. The mortar has high strength, does not unmix, has good surface properties without adding sand and can be worked in slab thicknesses ≥10 mm.
A German patent of Salzig, Wilhelm, DE 2320785(A1)—1974 that discloses perlite aggregate in a lightweight concrete and a concrete manufacturing process uses additions of perlite to the concrete in the mixer as a substitute for styropore or other products and can be injected into the concrete in a steam mechanism. The concrete is emptied from the mixer at 50-70° C. allowing the perlite to expand fully. The concrete has good heat and sound insulation and fire resistant properties.
Finally, two U.S. patents of Smetana et al., U.S. Pat. Nos. 5,114,617 and 5,356,446 relate to a high strength structural perlite concrete and to a low density insulating and fire resistant perlite concrete, respectively. The '617 patent relates to a wet mix of from 8 to 60 percent cement, 0.5 to 20 percent smooth-surfaced, vesicular, expanded perlite, 5 to 30 percent water, 0 to 12 percent pozzolan, and fine aggregate and coarse aggregate as appropriate and available in the circumstances. The concrete provides superior bond to reinforcing strands. The smooth-surfaced, vesicular, expanded perlite is unique and novel.
The second Smetana et al. patent, U.S. Pat. No. 5,356,446 relates to a method of providing thermal insulation and fire-resistance to buildings, by filling voids or spaces in and around structural members with a low density thermally insulating and fire-resistant cementitious composition containing a high proportion of a relatively smooth-surfaced, vesicular, expanded perlite. The method includes placing a flexible, woven, fire-resistant bag in the space to be filled, so as to act as a containment vessel, pumping a cementitious composition into the bag to fill a space by conforming to the shape of the space, while the bag simultaneously contains the cementitious composition in the desired position, and allowing the composition to cure into a lightweight, fire-resistant, and thermally insulating concrete. The method is particularly useful in and directed to remedial, post-construction applications in occupied buildings